In the operation of internal combustion engines, by-products from the combustion chamber often blow by the piston and admix with the lubricating oil. Compounds generally employed to neutralize the acidic materials and disperse sludge within the lubricating oil are overbased, alkaline earth metal, sulphurised, hydrocarbyl-substituted phenates, salicylates, napthenates and sulphonates. The term "overbased" is generally used to describe metal salts in which the ratio of the number of equivalents of the metal moiety to the number of equivalents of the acid moiety is greater than 1:1, and is usually greater than 1.2:1 and may be as high as 4.5:1 or greater. In contrast, the equivalent ratio of a metal moiety to acid moiety in "normal" or "neutral" metal salts is 1:1, and in "low-based" salts it is less than 1:1. Thus, the overbased material usually contains greater than 20% in excess of the metal present in the corresponding neutral material. For this reason overbased metal salts have a greater capability for neutralising acidic matter than do the corresponding neutral salts, though not necessarily an increased detergency power.
For environmental reasons it has become desirable to minimise the amount of sulphur in such materials, due to the resulting sulphur dioxide emissions associated with lubricant combustion in service, as well as in additive production. In response to the perceived desirability of providing sulphur-free overbased metal salts suitable for use as detergent additives in lubricating oils EP 0 450 874 discloses a non-sulphurised overbased metal salt of a sulphur-free calixarene having a substituent hydroxyl group or groups available for reaction with a metal base and their preparation by reacting at elevated temperature:
(A) either (i) a sulphur-free calixarene having a substituent hydroxyl group or groups available for reaction with metal base, (ii) a low-based metal calixarate, (iii) a neutral metal calixarate or (iv) an overbased metal calixarate, PA1 (B) a metal base added either in a single addition or in a plurality of additions at intermediate points during the reaction, PA1 (C) a solvent comprising either: (C.sub.1) either (i) a polyhydric alcohol having 2 to 4 carbon atoms, (ii) a di-(C.sub.3 or C.sub.4) glycol, (iii) a tri-(C.sub.2 -C.sub.4) glycol or (iv) a mono-or poly-alkylene glycol alkyl ether of the formula: EQU R.sup.9 (OR.sup.10).sub.f O R.sup.11 (II) PA1 (D) carbon dioxide added subsequent to each addition of component (B). PA1 (I) forming a mixture of components (A) and (C); PA1 (II) adding a metal base (B) to the mixture of components (A) and (C), the addition of said metal base (B) to said mixture of (A) and (C) being in a single addition or in a plurality of additions, steps (I) and (II) being performed concurrently or sequentially; and PA1 (III) adding (D) carbon dioxide to the mixture of components (A), (B) and (C) subsequent to each addition of component (B). PA1 (i) a C.sub.6 to C.sub.100 carboxylic acid, PA1 (ii) a di- or polycarboxylic acid containing from 36 to 100 carbon atoms, PA1 (iii) a hydrocarbyl-substituted suilphonic acid, PA1 (iv) a hydrocarbyl-substituted salicylic acid, PA1 (v) a hydrocarbyl-substituted naphthenic acid or PA1 (vi) a hydrocarbyl-substituted phenol.
wherein in the formula (II) R.sup.9 is a C.sub.1 to C.sub.6 alkyl group, R.sup.10 is an alkylene group, e.g. of 1-6 or 2-4 carbon atoms, R.sup.11 is hydrogen or a C.sub.1 to C.sub.6 alkyl group and f is an integer from 1 to 6; either alone or in combination with either: (C.sub.2) a hydrocarbon solvent; or (C.sub.3) either (i) water, (ii) C.sub.1 to C.sub.20 monohydric alcohol, (iii) a C.sub.1 to C.sub.2 ketone, (iv) a C.sub.1 to C.sub.10 carboxylic acid ester or (v) an aliphatic, alicyclic or aromatic C.sub.1 to C.sub.20 ether; or (C.sub.4) a C.sub.1 to C.sub.4 monohydric alcohol, in combination with a hydrocarbon solvent; PA2 component (A) comprising either (i) a sulphur-containing calixarene having at least one substituent hydroxyl group available for reaction with a metal base or (ii) a low-based, neutral or overbased metal salt of a calixarene derived from a sulphur-containing calixarene having at least one substituent hydroxyl group available for reaction with said metal base, PA2 component (C) comprising a solvent comprising either component (C.sub.1) or (C.sub.2); PA2 component (C.sub.1) comprising either (i) a polyhydric alcohol having 2 to 4 carbon atoms, (ii) a di-(C.sub.3 or C.sub.4) glycol, (iii) a tri-(C.sub.2 -C.sub.4) glycol or (iv) a mono- or poly-alkylene glycol alkyl ether of the formula: EQU R.sup.9 (OR.sup.10).sub.f OR.sup.11 (II) PA2 component (C.sub.2) comprising a C.sub.1 to C.sub.4 monohydric alcohol in combination with a hydrocarbon solvent;
EP 0 755 988 discloses the use of sulphur-free calixarenes having a molecular weight of at least 1880 for achieving high AV (Alkalinity Values as measured by the method of ASTM D2896), typically of at least 370, for example about 450, and potentially as high as 500 or more.
While reasons exist for making sulphur-free products as described above, it is not necessary in all situations to have detergents which are entirely free of sulphur. With the present invention it has been discovered that AVs in excess of 400 can in fact be achieved at molecular weights below 1880 when the calixarene contains sulphur.